Reel to Reel Options

@zygat , I have owned or own most of the machines in your list. Most are 1/4 track consumer machines. The Otari 5050 can play 1/4 track and half track. The 5050 is the most robust machine in your list. With any of them you will need to be able to refurb them yourself or find a person who can do it. New caps, new pinch rollers, alignment, etc. But once you get through all that the sound is unbeatable. 

And you can go a step further and add an outboard tube tape head playback unit. 

From that list, Otari and Revox.  Those other may only be 7.5ips.  You want a maxhine that plays 15ips.  Also look at Technics, Tascam, Studer.  Please make sure it's at least 15ips.  So many Master tapes available for sale for the first time in history.  

I’ve brought back a couple of Technics RS-1500s and a Revox B77 MkII. From a tinkering perspective the Revox is definitely easier to open up, recap, and realign. The Technics takes more patience but makes up for it with playback flexibility, since it can handle both 2 and 4 track at 7.5 and 15 ips. For me 15 ips is where the magic really comes through.

Besides a full recap, another issue you’ll often run into with R2R decks is worn heads. The good news is most of them can be relapped to play like new, and this guide walks through the process: How To Relap Tape Heads in 4 Steps • Head Relapping Guide

If you’re curious about what’s available today in terms of new releases, there are actually quite a few labels still producing R2R albums. I keep a running directory here: Reel to Reel Tapes for Sale • Worldwide Label Directory

When it comes to choosing a deck, it really depends on what you want out of the format. If your goal is to enjoy modern master tape copies, it may be worth looking for a machine that runs at 15 ips, supports IEC equalization, and plays 2-track stereo. If you’re more interested in vintage pre-recorded tapes, then a 4-track machine at 7.5 ips with NAB equalization may be better.

Akai's have some weaknesses in their logic control circuits (I know - I have a GX-620). Do you want two-track or four-track? If two-track, stick to Ampex 351 or AG-440, TASCAM or Otari. Four track means to me TEAC or Pioneer. Crown SX-8XX series can be either two- or four-track (second number in model means # of channels; third, # of tracks: an SX-824 is two-channel, four track. The 8 series is solid state. As they were designed to be used in remote locations, they're built like absolute tanks. ReVox B77's seem to be pretty good but the A77 has some built-in weaknesses in the transport from what I've been told by a r2r tech.

I have considered myself an audiophile since the late 60s, I have owned  many open real take decks throughout the years, my favorite has always been my Technics 1500US, I own one now and have two head blocks the original head block to record and two track and playback for track and I have the 1506 head block to record and for track and playback to track. That is very versatile and sounds great. I also have a Pioneer 707 that I use for background music. I am  80 years old and my ears aren’t what they Used to be but I still enjoy my music.